Respirators are commonly worn over the breathing passages of a person for at least one of two common purposes: (1) to prevent impurities or contaminants from entering the wearer's breathing track; and (2) to protect other persons or things from being exposed to pathogens and other contaminants exhaled by the wearer. In the first situation, the respirator is worn in an environment where the air contains particles that are harmful to the wearer, for example, in an auto body shop. In the second situation, the respirator is worn in an environment where there is risk of contamination to other persons or things, for example, in an operating room or a clean room.
A variety of respirators have been designed to meet either (or both) of these purposes. Some respirators have been categorized as being “filtering face-pieces” because the mask body itself functions as the filtering mechanism. Unlike respirators that use rubber or elastomeric mask bodies in conjunction with attachable filter cartridges (see, e.g., U.S. Pat. RE 39,493 to Yuschak et al.) or insert-molded filter elements (see, e.g., U.S. Pat. No. 4,790,306 to Braun), filtering face-piece respirators are designed to have the filter media cover much of the whole mask body so that there is no need for installing or replacing a filter cartridge. Filtering face-piece respirators commonly come in one of two configurations: molded respirators and flat-fold respirators.
Molded filtering face piece respirators have regularly comprised non-woven webs of thermally-bonded fibers or open-work plastic meshes to furnish the mask body with its cup-shaped configuration. Molded respirators tend to maintain the same shape during both use and storage. Examples of patents that disclose molded, filtering, face-piece respirators include U.S. Pat. No. 7,131,442 to Kronzer et al, U.S. Pat. Nos. 6,923,182, 6,041,782 to Angadjivand et al., U.S. Pat. No. 4,850,347 to Skov, U.S. Pat. No. 4,807,619 to Dyrud et al., U.S. Pat. No. 4,536,440 to Berg, and Des. 285,374 to Huber et al. Flat-fold respirators—as their name implies—can be folded flat for shipping and storage. Examples of flat-fold respirators are shown in U.S. Pat. Nos. 6,568,392 and 6,484,722 to Bostock et al. and in U.S. Pat. No. 6,394,090 to Chen.
During use, filtering face-piece respirators should maintain their intended cup-shaped configuration. After being worn numerous times and being subjected to high quantities of moisture from a wearer's exhalations—in conjunction with having the mask body bump into other objects while being worn on a person's face—known masks can be susceptible to collapsing or having an indentation pressed into the shell. A collapsed mask may be uncomfortable to the wearer, particularly if the indentation touches the nose or face. The wearer can remove the indentation by displacing the mask from their face and pressing on the indentation from the mask interior. To preclude masks from collapsing during use, additional layers have been added to the mask body structure to improve its structural integrity. U.S. Pat. No. 6,923,182 to Angadjivand et al., for example, uses first and second adhesive layers between the filtration layer and first and second shaping layers to provide a crush-resistant molded filtering face mask. To preserve the structural integrity of a flat-fold respirator, U.S. Pat. No. 6,394,090 to Chen provides first and second lines of demarcation on the mask body to assist in preventing collapse during use. U.S. patent application Ser. No. 12/562,239 to Spoo et al. uses four enclosed weld patterns on four quadrants of the mask body to achieve a collapse resistant structure. In known filtering face-piece respirators that use weld lines to enhance mask body structural integrity, the weld lines used are “single” in their application—that is, there are not pairs or groupings of closely-spaced parallel lines that work in concert with each other.